The Feasibility Study of the Octane-Enhancing Process: Isobutylene Dimerization Using C₄Mixture

Abstract

The dimerization of isobutylene to diisobutylene in C4 mixture was evaluated using various catalysts such as nickel salts system, zeolite system and acidic ion exchange resin. There were shown that the strong acidic type ion exchange resin (Amberlyst 15) under 6 kg/cm2 and 60 degrees C gave rise to 90% conversion and more than 60% selectivity to diisobutylene with acceptable amounts of oligomer as a best catalyst. Therefore, Amberlyst 15 was employed to investigate the optimum reaction condition. In the batch reaction, since the catalyst activity was increased with the increasing reaction temperature, the reaction time should be shortened appropriately to prevent a high yield of oligomer. The reaction rate was increased by the increased amount of catalyst without much change in the product composition. The formation of oligomer was inhibited when a small amount of organic solvents (methyl tert-butyl ether) are attended. In the fixed-bed study, the results indicate that the increase in reaction temperature was accompanied by the increase in reaction rate, however, the selectivity to the dimer was affected. Higher WHSV will enhance the selectivity but reduce the conversion. Conclusively, the appropriate reaction condition was 45 degrees C with WHSV of 10.

Alkenes oligomerization with resin catalysts

“…In the presence of TBA selectivity and conversion results were similar for monosulfonated (Amberlyst-15 and -16) and hypersulfonated (Amberlyst-35 and -36) resins, despite the higher acidity of the later (Table 1) [11]. However, with methanol as the selectivity enhancer the best performance was provided by Amberlyst-35 [44] whereas without polar additives Amberlyst-15 was stable and delivered the best results [53,93]. With the surface sulfonated resin Amberlyst-XE586 conversion was lower but selectivity was higher [11,44].…”

“…Generally the resins provided higher activity because the Lewis acid centers of the inorganic acid catalysts inhibit the dimerization reaction [123]. DOWEX HCR-W2, a hydrated gel type polystyrene based sulfonic acid resin was inactive at room temperature and scarcely active at reflux temperature (389 K) in accordance with the behavior of other gel type resins for alkene oligomerization [11,22,41,53,93]. Nafion and Amberlyst-15 although inactive at room temperature were both effective at reflux catalyzing the isomerization and dimerization of 2-ethyl-hex-1-ene [123].…”

“…Nafion provided the best results towards dimerization (90% yield at 389 K). As reported earlier higher temperatures have a negative impact on dimer yield (trimers were detected [124]) and promote formation of heavier oligomers [22,42,80,93].…”

“…Accessibility to the active sites is crucial and this is the reason why gel-type resins are unsuitable oligomerization catalysts [11,53]. Huang et al [93] confirmed the supremacy of macroreticular resins (e.g. Amberlyst-15 and -XN1010) in comparison with gel-type resins (e.g.…”

“…Amberlyst-15 and -XN1010) in comparison with gel-type resins (e.g. Amberlite-IR118 and IR120) from a kinetic perspective (conversion and selectivity were both higher) but also due to higher mechanical resistance [93].…”